Three-phase power meter monitoring for star and delta configurations

ABSTRACT

A three-phase power meter can monitor power on both 3-wire and 4-wire power lines. The power meter measures at least two voltages between phase conductors of the power line, and at least one voltage between a phase conductor and a neutral conductor of the power line when the neutral conductor is available. Using at least some of the measured voltages, the power meter can then operate in a first mode when coupled to a 3-wire power line to determine power on the power line based on the measured voltages, or operate in a second mode when coupled to a 4-wire power line to determine power on the power line based on the measured voltages.

FIELD OF THE DISCLOSURE

The present disclosure relates to a power meter for monitoring power ona three-phase power line.

BACKGROUND

In electrical power systems, a power source may deliver power to a loadover a three-phase power line. In general, there are two types ofthree-phase power line: 3-phase 4-wire power lines (also known as “star”or “wye” configuration), and 3-phase 3-wire power lines (also known as“delta” configuration). A 4-wire power line comprises three phaseconductors A, B and C, and a neutral conductor N. A 3-wire power linecomprises three phase conductors A, B and C, and no neutral conductor N.

Power meters may employ Blondel's Theorem when monitoring the power on a4-wire or 3-wire power line. A power meter for monitoring a 4-wire powerline may include circuitry to measure voltages on each of the threephase conductors with reference to the neutral conductor, and thecurrents on each phase conductor, in order to determine power. A powermeter for monitoring a 3-wire power line may include circuitry tomeasure voltages on two of the phase conductors with reference to athird phase conductor, and currents on two of the phase conductors, inorder to determine power.

Power meter manufacturers therefore manufacture different power meterswith different circuitry for each type of power line due to thedifferent voltage and current measurement requirements. This results inhigh manufacturing and production costs.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a three-phase power meter for monitoringpower on both 3-wire and 4-wire power lines. The power meter measures atleast two voltages between phase conductors of the power line, and atleast one voltage between a phase conductor and a neutral conductor ofthe power line when the neutral conductor is available. Using at leastsome of the measured voltages, the power meter can then operate in afirst mode when coupled to a 3-wire power line to determine power on thepower line based on the measured voltages, or operate in a second modewhen coupled to a 4-wire power line to determine power on the power linebased on the measured voltages.

In a first aspect of the present disclosure, there is provided athree-phase power meter comprising front-end circuit (FEC). The FEC isconfigured for coupling to a three wire or a four wire three-phase powerline comprising a plurality of conductors. The FEC is also configured togenerate a plurality of signals indicative of voltages betweenrespective pairs of conductors. The power meter further comprises aprocessing unit. The processing unit is coupled to the FEC, andconfigured to receive the plurality of signals, and to determine thepower of the three-phase power line. The power meter is configured tooperate in a first mode, in order to determine the power of a three wirethree-phase power line, and in a second mode, in order to determine thepower of a four wire three-phase power line.

In a second aspect of the present disclosure, there is provided afront-end circuit (FEC) for use in a three-phase power meter. The FEC isconfigured for coupling to a three wire or a four wire three-phase powerline comprising a plurality of conductors, and to generate a pluralityof signals indicative of voltages between respective pairs of conductorsof the three-phase power line, such that the three-phase power meter maydetermine a power of a three-phase three-wire power line in a firstmode, and determine a power of a three-phase four-wire power line in asecond mode.

In a third aspect of the present disclosure, there is provided a methodof determining the power of a three wire or a four wire three-phasepower line using a three-phase power meter, the three-phase power linecomprising a plurality of conductors. The method comprises steps of:receiving, using a processing unit, a plurality of signals indicative ofvoltages between respective pairs of conductors; determining whether thethree-phase power meter is coupled to a three wire power line or a fourwire power line; processing the plurality of signals, using theprocessing unit, in order to determine the power on the three-phasepower line, wherein the manner in which the plurality of signals areprocessed is dependent upon whether the meter is coupled to a three wireor four wire power line.

In a fourth aspect of the present disclosure, there is provided aprocessing unit arranged to carry out the method of the third aspect ofthe present disclosure.

Further features, embodiments, examples, and advantages of the presentdisclosure will be apparent from the following description and from theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a three-phase power line metering environment and athree-phase power meter in accordance with an embodiment of the presentdisclosure;

FIG. 2 shows front end circuitry (FEC) of a three-phase power meter inaccordance with an embodiment of the present disclosure;

FIG. 3 shows a processing unit of a three-phase power meter inaccordance with an embodiment of the present disclosure;

FIG. 4 shows an operational flow diagram of a three-phase power meter inaccordance with an embodiment of the present disclosure;

FIG. 5 shows components of a processing unit in accordance with anembodiment of the present disclosure;

FIGS. 6(a)-(c) show conceptual diagrams of three-phase power lines; and

FIG. 7 shows front end circuitry (FEC) of a three-phase power meter inaccordance with a further embodiment of the present disclosure.

DETAILED DESCRIPTION

In an approach, separate power meters are used for monitoring 3-phase4-wire and 3-phase 3-wire power lines. This is due to the powercalculations for each type of power line using different voltagemeasurements. The power calculation for a 3-phase 4-wire line usesvoltages measured at each phase conductor A, B, C, with reference to theneutral conductor N. This is illustrated, for example, in FIG. 6(a).Although the voltage on each power line conductor is time-varying, theinstantaneous values of the voltages between the phase conductors A, B,C and neutral N are denoted as V_(AN), V_(BN), V_(CN). Hence, 3-phase4-wire power meters may be specifically configured to measure thevoltages V_(AN), V_(BN), V_(CN).

The power calculation for a 3-phase 3-wire line uses the voltagesmeasured at two of the phase conductors with reference to another phaseconductor. For example, the power calculation for a 3-phase 3-wire linemay use the voltages measured at the phase conductors A, C withreference to the remaining phase conductor B. This is illustrated, forexample, in FIG. 6(b), where V_(AB) and V_(CB) denote instantaneousvoltages between the phase conductors A and B, and C and B,respectively. Hence, 3-phase 3-wire power meters may be specificallyconfigured to measure the voltages V_(AB), and V_(CB). 3-phase 3-wiremeters may similarly determine power by measuring voltages at the phaseconductors B, C with reference to the phase conductor A, or by measuringvoltages at the phase conductors A, B with reference to the phaseconductor C.

In any case, power meters for 3-wire and 4-wire power lines requiredifferent circuitry and hardware to measure the completely differentsets of voltages (V_(AN)/V_(BN)/V_(CN) or V_(AB)/V_(CB)) for therespective power computations. Manufacturers therefore produce separatepower meters for 3-wire and 4-wire scenarios.

The present disclosure relates to a three-phase power meter that can beused to monitor both 3-phase 3-wire power lines and 3-phase 4-wire powerlines. In particular, the power meter of the present disclosure isconfigured to measure a combination of voltages across the power lineconductors which can be used to determine the power of a three-phasepower line in both 3-wire and 4-wire scenarios. The power meter isconfigured to then operate in a 3-wire mode to determine the power onthe power line based on the measured voltages, or operate in a 4-wiremode to determine the power on the power line based on the measuredvoltages.

The power meter of the present disclosure is arranged to measure thevoltages at the phase conductors A, C with reference to the remainingphase conductor B (V_(AB) and V_(CB)). Furthermore, the power meter isalso arranged to measure the voltage between the phase conductor B andthe neutral conductor N (V_(BN)) when the neutral conductor isavailable. This is illustrated, for example, in FIG. 6(c). The powermeter also measures the current on each phase conductor.

When the power meter is coupled to a 3-wire power line, the power metermay operate in the first mode and determine the power based on thevoltages V_(AB) and V_(CB). In this case, a neutral conductor is notcoupled to the power meter, and therefore the voltage V_(BN) is notused, similar to FIG. 6(b). Nevertheless, the voltage V_(BN) is notnecessary for determining the power in a 3-wire scenario.

When the power meter is coupled to a 4-wire power line, the power metermay operate in the second mode to determine the power based on thevoltages V_(AB), V_(CB) and V_(BN). In this case, a neutral conductor iscoupled to the power meter, and the voltage V_(BN) is used. Based on theinstantaneous voltages V_(AB), V_(CB) and V_(BN), the power meter firstdetermines the instantaneous voltages V_(AN) and V_(CN). V_(AN) may bedetermined as V_(AN)=V_(AB)+V_(BN). V_(CN) may be determined asV_(CN)=V_(CB)+V_(BN). The power meter may then determine the power onthe 4-wire line using the measured voltage V_(BN), and the determinedvoltages V_(AN) and V_(CN), similar to FIG. 6(a).

The present disclosure therefore provides a power meter that can be usedin both 3-wire and 4-wire scenarios. The power meter avoids the need tomeasure completely different sets of voltages in each scenario. Rather,the power meter is configured to measure the voltages V_(AB), V_(CB),V_(BN) as shown in FIG. 6(c), and uses at least some of those voltagesto determine the power based on its operating mode. Advantageously, thepower meter of the present disclosure allows for a reduction inmanufacturing, product management, and storage costs associatedproducing two separate power meters for each 3-wire and 4-wire scenario.

Embodiments of the present disclosure are described in more detail asfollows.

FIG. 1 shows a three-phase power meter 100 in accordance with anembodiment of the present disclosure.

The meter 100 is arranged for coupling to a three-phase power line. Asshown in the example of FIG. 1, a three-phase power line 110 maycomprise phase conductors A, B, and C, and a neutral conductor N. Thisis also known as a 3-phase 4-wire power line. The meter 100 may becoupled to the three-phase power line 110 between a power source 120 anda load 130. Phase conductors of power lines are the conductors thatdeliver current and power to the load. In the case of a 4-wire powerline, the neutral conductor is usually the common reference point forthe load which may be connected to ground at the load.

The meter 100 comprises a plurality of terminals 101A, 102A, 101B, 102B,101C, 102C, 101N and 102N for coupling to the three-phase power line110. The plurality of terminals 101A, 101B, 1010 and 101N may beconsidered as input terminals, and the terminals 102A, 102B, 102C and102N may be considered as output terminals.

The input terminals 101A, 101B, 101C and 101N are arranged to receiveand couple to respective conductors from the source 120 side of thethree-phase power line 110. The terminal 101A is arranged to receive thephase conductor A from the source 120 side of the three-phase power line110. Furthermore, the terminal 101B is arranged to receive the phaseconductor B, the terminal 101C is arranged to receive the phaseconductor C, and the terminal 101N is arranged to receive the neutralconductor N from the source 120 side of the three-phase power line 110.

The output terminals 102A, 102B, 102C and 102N are arranged to receiveand couple to respective conductors from the load 130 side of thethree-phase power line 110. The terminal 102A is arranged to receive thephase conductor A from the load 130 side of the three-phase power line110. Furthermore, the terminal 102B is arranged to receive the phaseconductor B, the terminal 102C is arranged to receive the phaseconductor C, and the terminal 102N is arranged to receive the neutralconductor N from the load 130 side of the three-phase power line 110.

Therefore, the meter 100 may be connected to the power line 110 at apoint on the three-phase power line 110 between the power source 120 andthe load 130. Furthermore, as explained in more detail below, the meter100 is arranged such that a current flow I_(A), I_(B), I_(C), I_(N) oneach conductor A, B, C and N between the source 120 and load 130 ispermitted whilst the meter 100 is coupled to the power line 110.Connecting the meter 100 to the power line 110 may involve creating abreak in each conductor and coupling each side of the broken conductorto the meter 100 as described above.

The three-phase power line 110 in the example of FIG. 1 is shown havingthree phase conductors A, B, and C, and a neutral conductor N. This isalso referred to as a 3-phase 4-wire power line or a “star” or “wye”configuration. The meter 100 may also be coupled to a three-phase powerline having three phase conductors A, B and C, and no neutral conductorN, otherwise referred to as a 3-phase 3-wire power line, or a “delta”configuration. In the case of a 3-phase 3-wire line, the terminals 101A,102A, 101B, 102B, 101C, 102C may be coupled to the phase conductors asdescribed above. However, the terminals 101N and 102N may be leftuncoupled or floating due to absence of a neutral conductor.

FIG. 2 shows front end circuitry (FEC) 200 of the three-phase powermeter 100 according to an embodiment of the present disclosure. The FEC200 is arranged to couple or interface with the power line 110 via theterminals of the meter 100. The FEC 200 is arranged to output signalsindicative of voltages between conductors of the power line, andindicative of currents on the conductors of the power line. As describedin more detail below, the FEC 200 is configured to provide the outputsignals at voltage levels suitable for measuring by a processing unit.

The FEC 200 comprises a plurality of current sensors 240, 250 and 260.Each current sensor 240, 250 and 260 is arranged between respectivepairs of the input and output terminals of the meter 100. Each currentsensor is arranged to output a voltage signal indicative of a currentflowing between the respective input and output terminals of the meter100.

The current sensor 240 is arranged between the input terminal 101A andthe output terminal 102A. The current sensor 240 permits a current flowI_(A) between the input terminal 101A and the output terminal 102A, suchthat the current flow I_(A) between the input terminal 101A and theoutput terminal 102A is uninterrupted by the current sensor 240. Hence,when the terminals 101A and 102A are coupled to a phase conductor A of athree-phase power line, the current flow I_(A) from the power source120, through the conductor A and the meter 100 and to the load 130, willnot be interrupted.

The current sensor 240 comprises output nodes 241 and 242. The currentsensor 240 is configured to produce a voltage signal V_(IA)′ across theoutput nodes 241 and 242 in response to the current I_(A) flowingbetween the terminals 101A and 102A. As such, the voltage signal V_(IA)′across the output nodes 241 and 242 is indicative of the current I_(A)flowing between the terminals 101A and 102A. Furthermore, when the meter100 is coupled to a three-phase power line as shown in FIG. 1 orotherwise, the current I_(A) corresponds to the current flowing throughthe phase conductor A of the power line. Therefore, the voltage signalV_(IA)′ across the output nodes 241 and 242 may be indicative of thecurrent I_(A) flowing through the phase conductor A.

The current sensor 250 is arranged between the input terminal 101B andthe output terminal 102B. The current sensor 250 substantiallycorresponds to the current sensor 240 described above. As such, avoltage signal V_(IB)′ across output nodes 251 and 252 is indicative ofthe current I_(B) flowing between the terminals 101B and 102B.Furthermore, when the meter 100 is coupled to a three-phase power lineas shown in FIG. 1 or otherwise, the current I_(B) corresponds to thecurrent flowing through the phase conductor B of the power line.Therefore, the voltage signal V_(IB)′ across the output nodes 251 and252 may be indicative of the current I_(B) flowing through the phaseconductor B.

The current sensor 260 is arranged between the input terminal 101C andthe output terminal 102C. The current sensor 260 substantiallycorresponds to the current sensors 240 and 250 as described above. Assuch, a voltage signal V_(IC)′ across output nodes 261 and 262 isindicative of the current I_(C) flowing between the terminals 101C and102C. Furthermore, when the meter 100 is coupled to a three-phase powerline as shown in FIG. 1 or otherwise, the current I_(C) corresponds tothe current flowing through the phase conductor C of the power line.Therefore, the voltage signal V_(IC)′ across the output nodes 261 and262 may be indicative of the current I_(C) flowing through the phaseconductor C.

In some embodiments, the current sensors 240, 250 and 260 may comprise acurrent transformer. In such embodiments, each current transformer maybe positioned around conductors between respective terminals of the FEC200. In particular, each current transformer may comprise a coil windingwrapped around an annular core. The annular core may be positionedaround the conductors between the respective terminals of the FEC 200.For example, the current sensor 240 may comprise a current transformerpositioned around the conductor between the terminals 101A and 102A, thecurrent sensor 250 may comprise a current transformer positioned aroundthe conductor between the terminals 101B and 102B, and the currentsensor 260 may comprise a current transformer positioned around theconductor between the terminals 101C and 102C. The voltage signals atthe output nodes of the current sensors may be the voltage between twoends of the coil winding. For example, the voltage signal V_(IA)′between output nodes 241 and 242 may be the voltage between the ends ofthe coil winding of the current sensor 240, the voltage signal V_(IB)′between output nodes 251 and 252 may be the voltage between the ends ofthe coil winding of the current sensor 250, and the voltage signalV_(IC)′ between output nodes 261 and 262 may be the voltage between theends of the coil winding of the current sensor 260. In some embodiments,the current transformer of each current sensor may be a Rogowski coil.

In the above description, the current transformers of the currentsensors 240, 250 and 260 have been described as being arranged internalto the FEC 200 around the conductors between the terminals 101 and 102.In some embodiments, the current transformers may be coupled directlyaround the phase conductors of the three-phase power line. For example,with reference to FIG. 1, the current transformers may be coupleddirectly around each phase conductor A, B, C, external to the meter 100.In any case, the current transformers may be coupled around anyconductor carrying the respective currents I_(A), I_(B) and I_(C) inorder to sense those currents.

In further embodiments, the current sensors may each comprise a shuntresistor. In such embodiments, each shunt resistor may be arranged inseries between the respective terminals of the meter 100 and FEC 200.For example, the current sensor 240 may comprise a shunt resistorbetween the terminals 101A and 102A, the current sensor 250 may comprisea shunt resistor between the terminals 101B and 102B, and the currentsensor 260 may comprise a shunt resistor between the terminals 101C and102C. The voltage signals at the output nodes of the current sensors maybe the voltage across the respective shunt resistor. For example, thevoltage signal V_(IA)′ between output nodes 241 and 242 may be thevoltage across the shunt resistor of the current sensor 240, the voltagesignal V_(IB)′ between output nodes 251 and 252 may be the voltageacross the shunt resistor of the current sensor 250, and the voltagesignal V_(IC)′ between output nodes 261 and 262 may be the voltageacross the shunt resistor of the current sensor 260. Each shunt resistormay be small valued. For example, the shunt resistor may range from 100μΩ to several mΩ. The shunt resistor may be chosen as any suitable valuedepending on the current and power dissipation limits of the power lineusing known techniques.

In other embodiments, the current sensors may comprise hall-effectcurrent sensors for sensing the current on each phase conductor. Anyother type of current sensor known in the art may also be used toproduce the voltage signals V_(IA)′ V_(IB)′ and V_(IC)′ indicative ofthe currents I_(A), I_(B), I_(C).

As shown in FIG. 2, there is no current sensor provided between theneutral terminals 101N and 102N. Rather, the neutral terminals 101N and102N are directly short circuited. Hence, when the meter is coupled to athree-phase power line having a neutral conductor, the meter may permitthe current flow I_(N) between the terminals 101N and 102B, andtherefore the current flow I_(N) through the neutral conductor N of thethree-phase power line. In some embodiments, the meter 100 may bearranged to sense the neutral current I_(N), which is explained in moredetail below.

The front end circuitry 200 further comprises a plurality of voltagedividers 210, 220 and 230. Each voltage divider is arranged between arespective pair of the input terminals 101A, 101B, 101C and 101N. Eachvoltage divider is arranged to output a signal indicative of the voltageacross the respective pair of the input terminals. When the meter 100 iscoupled to a power line, such as the power line 110 in FIG. 1 orotherwise, each voltage divider outputs a signal indicative of thevoltage across the respective pair of power line conductors.

The voltage divider 210 is arranged between the input terminals 101A and101B. The voltage divider 210 comprises two resistors R₂₁₁ and R₂₁₂. Theresistors R₂₁₁ and R₂₁₂ are arranged in series between the inputterminals 101A and 101B. The voltage divider 210 also comprises anintermediate node 213 at a common point between the resistors R₂₁₁ andR₂₁₂. The voltage divider 210 is arranged to divide a voltage V_(AB),where V_(AB) is the voltage across the terminals 101A and 1018. Thedivided voltage is provided as the voltage signal V_(AB)′ at theintermediate node 213, for example, when referenced to the terminal101B. By virtue of the resistor arrangement, the voltage divider may becharacterised by the equation:V _(AB) ′=V _(AB) *R ₂₁₂/(R ₂₁₁ +R ₂₁₂)

The voltage signal V_(AB)′ at the intermediate node 213 is thereforeindicative of the voltage V_(AB) across the terminals 101A and 101B.Furthermore, when the meter 100 is coupled to a three-phase power lineas shown in FIG. 1 or otherwise, the voltage signal V_(AB) across theterminals 101A and 101B corresponds to the voltage across the phaseconductors A and B of the power line. Therefore, the voltage signalV_(AB)′ at the intermediate node 213 may be indicative of the voltageV_(AB) across the phase conductors A and B of the three phase powerline.

The values of the resistors in the voltage divider 210 and the resultingvoltage division may be chosen appropriately using known techniques,such that the divided voltage can be measured by other components of themeter 100, whilst also meeting the safety and maximum ratings of thosecomponents. For example, the values of the resistors may be chosen suchthat the voltages can be measured by the processing unit 300 and itscomponents described below, whilst also meeting their safety and maximumratings. In one example, the resistor R211 may be in the range of 1 kΩor more, and the resistor R212 may be in the range of 1 MΩ or more.

The voltage divider 220 is arranged between the input terminals 101B and101N and comprises resistors R₂₂₁ and R₂₂₂. The arrangement of thevoltage divider 220 is substantially similar to the arrangement of thevoltage divider 210 and is therefore characterised by a similar equationand similar resistor values. The voltage divider 220 is thereforearranged to divide a voltage V_(BN), where V_(BN) is the voltage acrossthe terminals 101B and 101N. The divided voltage is provided as thevoltage signal V_(BN)′ at the intermediate node 223, for example, whenreferenced to the terminal 101N. The voltage signal V_(BN)′ at theintermediate node 223 is therefore indicative of the voltage V_(BN)across the terminals 101B and 101N. Furthermore, when the meter 100 iscoupled to a 4-wire three-phase power line as shown in FIG. 1, thevoltage V_(BN) across the terminals 101B and 101N corresponds to thevoltage across the phase conductor B and neutral conductor N of thepower line. Therefore, the voltage signal V_(BN)′ at the intermediatenode 223 may be indicative of the voltage V_(BN) across the phaseconductor B and neutral conductor N of the three phase power line.

The voltage divider 230 is arranged between the input terminals 101C and101B and comprises resistors R₂₃₁ and R₂₃₂. The arrangement of thevoltage divider 230 is substantially similar to the arrangement of thevoltage dividers 210 and 220, and is therefore characterised by asimilar equation and similar resistor values. The voltage divider 230 istherefore arranged to divide a voltage V_(CB), where V_(CB) is thevoltage across the terminals 101C and 101B. The divided voltage isprovided as the voltage signal V_(CB)′ at the intermediate node 233, forexample, when referenced to the terminal 101B. The voltage V_(CB)′ atthe intermediate node 233 is therefore indicative of the voltage V_(CB)across the terminals 101B and 101B. Furthermore, when the meter 100 iscoupled to a three-phase power line as shown in FIG. 1 or otherwise, thevoltage V_(CB) across the terminals 101C and 101B corresponds to thevoltage V_(CB) across the phase conductors C and B of the power line.Therefore, the voltage signal V_(CB)′ at the intermediate node 233 maybe indicative of the voltage V_(CB) across the phase conductors C and Bof the three phase power line.

Although FIG. 2 shows two resistors in each voltage divider, it shouldbe appreciated that other component arrangements may be used to form thevoltage dividers. For example, each resistor shown in FIG. 2 may bereplaced by a network of series and/or parallel resistors to achieve thedesired voltage division at the intermediate nodes. Furthermore,components other than resistors suitable for use in voltage dividers mayalso be used, including capacitors, inductors or transistors. Forexample, as shown in FIG. 7 and described in more detail below, thevoltage dividers may be replaced with voltage transformers.

FIG. 3 shows a processing unit 300 in accordance with an embodiment ofthe present disclosure. The processing unit 300 may be included in thepower meter 100 of FIG. 1 as described above, with the FEC 200 of FIG.2. The processing unit 300 is configured to receive the output signalsfrom the FEC 200. Based on the received signals, the processing unit isconfigured to determine and monitor the power of a power line that iscoupled with the meter 100, such as the power line 110 in FIG. 1 orotherwise.

The processing unit 300 comprises a plurality of differential inputs: V1p, V1 n, V2 p, V2 n, V1 p, V3 n, I1 p, I1 n, I2 p, I2 n, I3 p, and I3 n.The pairs of differential inputs V1 p/V1 n, V2 p/V2 n, and V3 p/V3 n arefor receiving voltage signals indicative of the voltages betweenconductors of the power line being monitored. The pairs of differentialinputs I1 p/I1 n, I2 p; I2 n, and I3 p/I3 n are for receiving voltagesignals indicative of the current flowing through the phase conductorsof the power line being monitored. The processing unit 300 is arrangedto measure the signals received at the positive inputs (e.g. V1 p, I1p), with reference to the respective negative inputs (e.g. V1 n, I1 n).

FIG. 3 shows how the inputs of the processing unit 300 are coupled tothe nodes of the FEC 200 when included in the meter 100.

The positive input V1 p is coupled to the intermediate node 213 of thevoltage divider 210. The corresponding negative input V1 n is coupled tothe terminal 1018. The processing unit 300 is therefore arranged toreceive the divided voltage signal V_(AB)′ that is indicative of thevoltage V_(AB) between the terminals 101A and 101B, i.e. between thephase conductors A and B of the 3 or 4 wire three-phase power line beingmonitored.

The positive input V2 p is coupled to the intermediate node 223 of thevoltage divider 220. The corresponding negative input V2 n is coupled tothe terminal 101N. The processing unit is therefore arranged to receivethe divided voltage signal V_(BN)′ that is indicative of the voltageV_(BN) between the terminals 101B and 101N, i.e. between the phaseconductor B and neutral conductor N of the three-phase power line whenthe meter 100 is coupled to a 4-wire power line.

The positive input V3 p is coupled to the intermediate node 233 of thevoltage divider 230. The corresponding negative input V3 n is coupled tothe terminal 1018. The processing unit is therefore arranged to receivethe divided voltage signal V_(CB)′ that is indicative of the voltageV_(CB) between the terminals 101C and 101B, i.e. between the phaseconductors C and B of the 3 or 4 wire three-phase power line beingmonitored.

The positive input I1 p is coupled to the node 241, and the negativeinput I1 n is coupled to the node 242 of the current sensor 240. Theprocessing unit is therefore arranged to receive the voltage signalV_(IA)′ indicative of the current I_(A) flowing between the terminals101A and 102A, i.e. the current flowing on the phase conductor A of the3 or 4 wire power line being monitored.

The positive input I2 p is coupled to the node 251, and the negativeinput I2 n is coupled to the node 252 of the current sensor 250. Theprocessing unit is therefore arranged to receive the voltage signalV_(IB)′ indicative of the current I_(B) flowing between the terminals101B and 102B, i.e. the current flowing on the phase conductor B of the3 or 4 wire power line being monitored.

The positive input I3 p is coupled to the node 261, and the negativeinput I3 n is coupled to the node 262 of the current sensor 260. Theprocessing unit is therefore arranged to receive the voltage signalV_(IC)′ indicative of the current I_(C) flowing between the terminals101C and 102C, i.e. the current flowing on the phase conductor C of the3 or 4 wire power line being monitored.

FIG. 4 illustrates the processing steps implemented by the processingunit 300 to determine and monitor the power of a 3 or 4 wire power linecoupled with the meter 100.

In summary, the processing unit 300 measures or senses voltage signalsreceived from the FEC 200. The measured or sensed voltage signals areindicative of voltages across the conductors of the power line beingmonitored, and indicative of currents through the phase conductors ofthe power line being monitored. The processing unit 300 is configured tothen operate in a first mode or a second mode of operation to determineand monitor a power of a three-phase power line coupled with the meter100. The processing unit 300 may operate in the first mode of operationwhen the meter 100 is coupled to a 3-phase 3-wire power line (i.e. athree-phase power line with three phase conductors A, B and C, and noneutral conductor N). The processing unit 300 may operate in the secondmode of operation when the meter 100 is coupled to a 3-phase 4-wirepower line (i.e. a three-phase power line with three phase conductors A,B and C, and a neutral conductor N, as shown in FIG. 1). The processingunit 300 employs specific computations and techniques to determine thepower of each type of power line, as described in more detail below.

At step S401, the processing unit 300 measures or senses the voltagesignals V_(AB)′, V_(BN)′, V_(CB)′, V_(IB)′, V_(IC)′ received from theFEC 200. The processing unit 300 may sample and convert the receivedvoltage signals into digital signals using a plurality ofanalog-to-digital converters (ADCs). When the meter is coupled to athree-phase power line, the voltage signals will be time varying, forexample, at fundamental or harmonic frequencies of the power line. Theprocessing unit 300 may therefore continuously receive and sample theinstantaneous voltage signals V_(AB)′, V_(BN)′, V_(CB)′, V_(IA)′,V_(IB)′, V_(IC)′ at a suitable sampling rate.

As indicated at step S403, the processing unit 300 is configured tooperate in a first mode or a second mode. In particular, at step S403,the processing unit 300 may determine whether the meter 100 is coupledto a 3-wire power line or a 4-wire power line. The processing unit 300may operate in the first mode of operation when the meter 100 is coupledto a 3-phase 3-wire power line, and in the second mode of operation whenthe meter 100 is coupled to a 4-wire power line.

In the first mode of operation, at step S405, the processing unit 300determines the actual instantaneous voltages V_(AB) and V_(CB), of thepower line. In some embodiments, the processing unit 300 may determinethe voltage V_(AB) by multiplying V_(AB)′ by a compensation gain tocompensate for the dividing effect of the voltage divider 210.Similarly, the processing unit 300 may determine the voltage V_(CB), bymultiplying V_(CB)′ by a respective compensation gain to compensate forthe dividing effect of the voltage divider 230.

The compensation gains may be pre-programmed into registers of theprocessing unit 300. The compensation gains may be based on the valuesof the resistors of each voltage divider. In some embodiments, eachcompensation gain may be determined and calibrated offline and stored inregisters of the processing unit 300. The calibration may involve:inputting a known voltage signal through a voltage divider, determiningthe divided voltage signal measured by the processing unit 300 (e.g. atthe output of the ADCs of the processing unit 300), and determining thecompensation gain as the gain between the known inputted signal andmeasured divided signal.

Furthermore, at step S405, the processing unit 300 determines the actualinstantaneous currents I_(A) and I_(C) of the power line. The currentI_(A) may be determined by multiplying V_(IA)′ by a conversion gain toconvert the voltage signal V_(IA)′ into the current I_(A). Similarly,the current I_(C) may be determined by multiplying V_(IC)′ by arespective conversion gain.

The conversion gains may be pre-programmed into registers of theprocessing unit 300 to be used when executing step S405. The conversiongains may be based on parameters of the current sensors 240 and 260,such as their impedance between the output nodes 241 and 242, and 261and 262. In some embodiments, each conversion gain may be determined andcalibrated offline and stored in registers of the processing unit 300.The calibration may involve: inputting a known current signal through acurrent sensor, determining the voltage signal measured by theprocessing unit 300 that is indicative of the current (e.g. at theoutput of the ADCs of the processing unit 300), and determining theconversion gain as the gain between the known inputted signal andmeasured signal.

At step S407, the processing unit 300 determines the power on the3-phase 3-wire line coupled with the meter 100 (i.e. the power beingconsumed or produced by the load). In accordance with Blondel's Theorem,if the phase conductor B is considered as a common reference point ofthe 3-wire line, the power of the 3-phase 3-wire line may be determinedusing the two voltages V_(AB) and V_(CB), and the two currents I_(A) andI_(C). Therefore, in the first mode of operation, the processing unit300 determines the power based on the determined instantaneous voltagesV_(AB) and V_(CB), and the determined instantaneous currents I_(A) andI_(C).

Different types of power quantities of the power line may be determinedusing the instantaneous voltages V_(AB), V_(CB) and currents I_(A),I_(C). For example, the instantaneous voltages and currents may be usedto determine one or more of the total active, reactive and apparentpowers on the power line. Furthermore, the instantaneous voltages andcurrents may also be used to determine one or more of the active,reactive and apparent powers of constituent frequency components ofpower transmission signals on the power line, such as the powers at thefundamental frequency and at individual harmonic frequencies of thepower transmission signals on the power line. The processing unit 300may be configured to employ any known technique of computing any one ormore of the above power quantities on the 3-phase 3-wire power line,based on the instantaneous voltages and currents V_(AB), V_(CB), I_(A),I_(C). As an example, computing the total active power on the 3-phase3-wire power line may involve first computing the instantaneous powersP_(A)=V_(AB)×I_(A) and P_(C)=V_(CB)×I_(C) on the respective phaseconductors A and C. The instantaneous powers P_(A) and P_(C) may then beused to determine power quantities P_(A-Active) and P_(C-Active) whichare the total active powers on the phase conductors A and Crespectively. In accordance with Blondes Theorem, computing the overalltotal active power P_(3w-Active) may involve summing the powerquantities P_(A-Active) and P_(C-Active). Any other additional,alternative or intermediate computational steps for computing the powermay be envisaged by the skilled person based on known techniques.Determining power quantities may also involve storing or registeringcurrent and past instantaneous voltage, current or power values for usein the power calculations.

At step S409, the processing unit 300 may output a signal indicative ofthe determined power, such as the total active power P_(3w-Active). Insome embodiments, the processing unit 300 may be in communication with adisplay device that receives the output signal and displays the powerquantity. The display device may be included in the meter 100, or beexternal to the meter 100. Alternatively or additionally, the processingunit 300 may be in communication with any other device for displaying,recording or analysing the determined powers.

The processing unit 300 may operate in the second mode of operation whenthe meter 100 is coupled to a 3-phase 4-wire power line. In the secondmode of operation, at step S415, the processing unit 300 determines theactual voltages and currents V_(AB), V_(CB), I_(A) and I_(C) asdescribed above. Furthermore, in the second mode of operation, theprocessing unit also determines the actual voltage V_(BN) and thecurrent I_(B). Similarly to determining V_(AB) and V_(CB), theprocessing unit 300 may determine the instantaneous voltage V_(BN) bymultiplying V_(BN)′ by a respective compensation gain to compensate forthe dividing effect of the voltage divider 220. Similarly to determiningI_(A) and I_(C), the processing unit 300 may determine the instantaneouscurrent I_(B) by multiplying V_(IB)′ by a respective conversion gain.The respective compensation gains and conversion gains may be determinedand/or pre-programmed into registers of the processing unit as describedabove.

At step S417, the processing unit 300 determines the instantaneousvoltages V_(AN) and V_(CN). The voltage V_(AN) corresponds to a voltagebetween a phase conductor A and a neutral conductor N of the 3-phase4-wire line being monitored, such as the power line shown in FIG. 1. Thevoltage V_(CN) corresponds to a voltage between a phase conductor C andthe neutral conductor N of the 3-phase 4-wire line being monitored.Since the voltages V_(AN) and V_(CN) are not directly measured by themeter 100, the processing unit 300 determines those voltages as:V _(AN) =V _(AB) +V _(BN)V _(CN) =V _(CB) +V _(BN)

Therefore, the instantaneous voltages V_(AN) and V_(CN) are madeavailable. The voltage V_(BN) is already available at this step as it ismeasured by the meter 100.

In the second mode of operation at step S419, the processing unit 300determines a power of the 3-phase 4-wire line coupled with the meter. Inaccordance with Blondel's Theorem, if the neutral conductor N isconsidered as a common reference point of the 4-wire line, the power maybe determined using the voltages V_(AN), V_(BN), V_(CN), and thecurrents I_(A), I_(B), I_(C). Therefore, in the second mode ofoperation, the processing unit 300 determines the power based on thedetermined instantaneous voltages V_(AN), V_(BN), V_(CN) and thedetermined instantaneous currents I_(A), I_(B) and I_(C).

As explained above, different power quantities of the power line may bedetermined based on the instantaneous voltages and currents. Theprocessing unit 300 may be configured to employ any known technique ofcomputing any one or more of the previously described power quantitieson a 3-phase 4-wire power line based on the instantaneous voltages andcurrents V_(AN), V_(BN), V_(CN), I_(A), I_(B), I_(C). As an example,computing the total active power may involve first computing theinstantaneous powers P_(A)=V_(AN)×I_(A), P_(B)=V_(BN)×I_(B), andP_(C)=V_(CN)×I_(C) on the respective phase conductors A, B and C. Theinstantaneous powers P_(A), P_(B), P_(C) may then be used to determinepower quantities P_(A-Active), P_(B-Active) and P_(C-Active) which arethe total active powers on each phase conductor A, B and C respectively.In accordance with Blondel's Theorem, computing the overall total activepower P_(4w-Active) may involve summing the powers P_(A-Active),P_(B-Active), P_(C-Active). Any other additional, alternative orintermediate computational steps for computing the power may beenvisaged by the skilled person. Determining power quantities may alsoinvolve storing or registering current and past instantaneous voltage,current or power values for use in the power calculations.

At step S421, similarly to step S409, the processing unit 300 may outputa signal indicative of the determined power, such as the total activepower P_(4w-Active). The signal may be outputted to the display deviceor any other device as described above.

In each mode of operation, the processing unit 300 may repeat the stepsin FIG. 4 to continuously monitor the power or any of the powerquantities on the 3-phase 3-wire or 3-phase 4-wire power line coupledwith the meter 100.

In some embodiments, the processing unit 300 may be configured toreceive user input to select the operating mode of the processing unit300. For example, the processing unit 300 may be in communication with auser input device (not shown). The user input device may be any deviceor controller that allows a user to select a first operating mode whenthe meter 100 is coupled to a 3-wire line, and select a second operatingmode when the meter 100 is coupled to a 4-wire line. At step S403 of themethod in FIG. 4, the processing unit 300 may check the user selectedmode and proceed with the method according to the first or second modeaccordingly. The user input device may be included in the meter 100, orbe external to the meter 100. In some examples, the user input devicemay be a switch, button, or a touchscreen device.

In other embodiments, the processing unit 300 may be configured toautomatically determine its operating mode. In particular, theprocessing unit 300 may be configured to automatically detect whetherthe meter 100 is coupled to a 3-phase 3-wire power line, or a 3-phase4-wire power line. If the processing unit 300 determines that it iscoupled to a 3-phase 3-wire line, the processing unit may automaticallyset itself to operate in the first operating mode. If the processingunit 300 determines that it is coupled to a 3-phase 4-wire line, theprocessing unit may automatically set itself to operate in the secondoperating mode.

In some embodiments, the processing unit 300 may determine whether it iscoupled to a 3-wire or 4-wire power line based on the magnitude of thevoltage signal V_(BN)′. The magnitude of V_(BN)′ may preferably bedetermined as the RMS of the voltage signal V_(BN)′, but may also bedetermined as the instantaneous peak value, or peak-to-peak magnitude. AV_(BN)′ magnitude of approximately 0V may indicate that the neutralterminals 101N and 102N of the meter 100 are not connected to a neutralconductor N. Therefore, it can be assumed that there is no neutralconductor present and that the meter 100 is coupled to a 3-wire powerline. Hence, the processing unit may compare the voltage signal V_(BN)′to a threshold value V_(T). If V_(BN)′ does not exceed the thresholdvalue V_(T), the processing unit 300 may determine it is coupled to a3-wire line and operate in the first mode of operation. Otherwise, ifV_(BN)′ exceeds the threshold value V_(T), the processing unit 300 maydetermine it is coupled to a 4-wire line and operate in the second modeof operation.

The threshold V_(T) may be any value appropriate for distinguishingwhether the meter 100 is coupled to a neutral conductor. V_(T) may bedetermined empirically during calibration of the meter 100, ortheoretically, using methods known to the skilled person. Furthermore,it may not be necessary to continuously determine the operating mode.Rather, in some embodiments, the processing unit 300 may automaticallydetermine the operating mode after a reset event (e.g. when theprocessing unit 100 is powered up or reset). The processing unit 300 maythen continue to operate in that operating mode when executing themethod in FIG. 4. The processing unit 300 may then re-determine theoperating mode only when another reset event occurs.

The processing unit 300 may be any processing device known to theskilled person that is suitable for performing or executing the methodsof the present disclosure. For example, in some embodiments, theprocessing unit 300 may be any microcontroller, microprocessor, logiccircuit, integrated circuit or combinations thereof. The processing unit300 may also be any three-phase metering integrated circuit that isconfigurable to perform the methods of the present disclosure. As such,the processing unit 300 may be implemented as a single integratedcircuit comprising components for executing the methods describedherein, such as anti-aliasing filters, analog-to-digital converters(ADCs), digital signal processors, storage registers, data interfaces,and control interfaces.

In some embodiments, the processing unit 300 may be implemented as aplurality of one or more integrated circuits (ICs). For example, asshown in FIG. 5, the processing unit 300 may comprise a plurality of ADCintegrated circuits (ADC-ICs) 501, 502, 503, and a digital processor IC504.

In the example of FIG. 5, an ADC-IC 501, 502, 503 is provided for eachphase conductor A, B and C of the three-phase power line beingmonitored. The ADC-IC 501 comprises the differential inputs V1 p, V1 n,I1 p and I1 n for coupling to nodes the front end circuitry 200. Thedifferential inputs may be coupled to nodes of the circuitry 200 asdescribed above and shown in FIG. 3 and as indicated by their likereference signs. Therefore, the ADC-IC 501 may receive signals from thefront end circuitry 200 at its differential inputs as already described.Furthermore, the differential inputs of the ADC-ICs 502 and 503 may alsobe coupled to nodes of the circuitry 200 and receive signals from thefront end circuitry 200 as already described above and as indicated bytheir like reference signs.

Each ADC-IC 501, 502, 503 is configured to convert the received signalsinto digital signals. The ADC-ICs may comprise an individual ADC foreach pair of differential inputs.

The ADC-ICs 501, 502, 503 are arranged to provide the digital signals tothe digital processor IC 504. The digital processor IC 504 is configuredto perform processing or operational steps in accordance with themethods of the present disclosure. For example, the digital processor IC504 may perform the calculations and operations described in respect ofFIG. 4.

The ADC-ICs 501, 502, 503 may be any type of ADC-IC that can be arrangedas shown in FIG. 5 and perform the operations described herein. In someembodiments, the ADC-ICs 501, 502, 503 may be isolated ADC-ICs providingan isolation barrier between the digital (output) side and analog(input) side of the ICs. The digital processor IC 504 may be any digitalprocessor IC or microprocessor configurable to interface with theADC-ICs and perform the steps of the methods of the present disclosure.

As such, the processing unit 300 may be implemented as a singleintegrated circuit, or as a plurality of one or more integratedcircuits.

Various modifications, variations and implementations of the presentdisclosure are now described as follows.

In some embodiments of the present disclosure, each voltage divider 210,220, 230 in the FEC 200 of FIG. 2 may be replaced with a voltagetransformer. FIG. 7 shows an example of a front end circuit (FEC) 700that comprises voltage transformers 710, 720, 730 in place of thevoltage dividers of the FEC 200 in FIG. 2. All other aspects of the FEC700 of FIG. 7 are similar to the FEC 200 of FIG. 2. The voltagetransformer 710 is arranged to receive input from the pair of terminals101A and 101B. The voltage transformer 710 is arranged to reduce or stepdown the voltage V_(AB) between the terminals 101A and 1018 to provide areduced voltage signal V_(AB)′ between its output terminals 713 a and713 b. The level of voltage reduction provided by the voltagetransformer 710 may be set by the turns-ratio between the primary andsecondary coil windings of the voltage transformer 710. The voltagetransformers 720 and 730 are similarly arranged to receive input fromthe respective pairs of terminals 101B/101N and 101C/101B, and to reduceor step down each voltage V_(BN) and V_(CB) to provide the reducedvoltage signals V_(BN)′ and V_(CB)′ between the voltage transformeroutputs 723 a/723 b and 733 a/733 b. When using the FEC 700 in the meter100, the processing unit 300 may be coupled to the FEC 700 differentlyto what is shown in FIG. 3 in order to receive the voltage signalsV_(AB)′, V_(B) and V_(CB)′. In particular, the differential inputs V1 pand V1 n may couple to the outputs 713 a and 713 b of the transformer710. Similarly, the differential inputs V2 p and V2 n may couple to theoutputs 723 a and 723 b of the transformer 720, and the differentialinputs V3 p and V3 n may couple to the outputs 733 a and 733 b of thetransformer 730. The remaining differential inputs may couple to the FEC700 as previous described with respect to the FEC 200. Subsequently, atsteps S405 and S415 of the method shown in FIG. 4, the processing unit300 may use or determine appropriate compensation gains as previouslydescribed in order to compensate for the step down or reducing effect ofthe voltage transformers and determine the actual voltages V_(AB),V_(CB) and V_(BN). Therefore, when using the FEC 700, the compensationgains may be dependent on the turns-ratios of the voltage transformers.The voltage dividers and voltage transformers of the present disclosuremay more generally be referred to as voltage generators.

In the present disclosure, the processing unit 300 has been described asmeasuring the voltage signal V_(AB)′ indicative of the voltage V_(AB) byreferencing the intermediate node 213 of the voltage divider 210 withrespect to the input terminal 101B. However, it should be appreciatedthat any other equivalent node may be used as a reference, such as theoutput terminal 102B, or any other equivalent node that has the sameelectrical potential level of the phase conductor B. Similarly, anyother equivalent nodes may be used as reference for measuring any othervoltage, such as the voltage signals V_(CB)′ and V_(BN)′, V_(IA)′,V_(IB)′, and V_(IC)′.

In some embodiments, the divided voltages may be measured by theprocessing unit 300 with respect to alternative reference nodes. Forexample, it has been described above how the voltage divider 220 isarranged to provide a divided voltage signal V_(BN)′ at the node 223when referenced to the neutral conductor N at the terminal 101N.However, the voltage divider 220 may be arranged in an opposite way toprovide a divided voltage signal V_(NB)′ at the node 223 when referencedto the phase conductor B. The processing unit 300 may be arranged tomeasure the divided signal V_(NB)′ by coupling the node 223 to thepositive input V2 p, and the terminal 101B (or any other node that hasthe same electrical potential as the phase conductor B) to the negativeinput V2 n. A respective compensation gain may be used accordingly todetermine the voltage V_(NB) at step S415 of the method in FIG. 4.Subsequently, the voltage V_(BN) may be determined as V_(BN)=−V_(NB) atstep S417 of the method in FIG. 4, and then V_(BN) used to determinepower as described at step S419. As such, the alternative referencingand voltage divider arrangement may be used to determine the voltageV_(BN). Measuring V_(NB)′ instead of V_(BN)′ allows for the phaseconductor B to be used as a common reference for all of the voltagesignals V_(AB)′, V_(CB)′ and V_(NB)′. This may allow the meter 100 to beimplemented with a processing unit 300 that only allows for a singlecommon reference input to all of the negative inputs. Nevertheless, insome embodiments, the voltages V_(BN), V_(AB) and V_(CB) may bedetermined using alternative referencing as described above in anycombination in order to meet the implementation requirements of theprocessing unit 300. For example, some implementations of the processingunit shown in FIG. 5 may require that each ADC-IC 501, 502, 503 isreferenced to the respective phase conductors A, B or C at the negativevoltage inputs V1 n, V2 n, V3 n, respectively, in order to achievebetter isolation between the conductors. Therefore, the voltage dividersof the FEC may be arranged such that the ADC-ICs measure the voltagesV_(BA)′, V_(BC)′ and V_(NB)′. These voltages may be compensated andnegated in order to determine the voltages V_(AB), V_(CB) and V_(BN) asdescribed above in order to determine power.

The voltage signals V_(IA)′, V_(IB)′, and V_(IC)′ indicative of currentsmay also be referenced in an opposite way at the respective positive andnegative inputs to the processing unit 300. Other equivalent oralternative means of referencing any of the measured signals may beenvisaged.

In the present disclosure, the meter 100 is arranged to determine powerbased on the determined voltages V_(AB), V_(CB) and V_(BN), where thephase conductor B is the common phase conductor between the pairs ofconductors and voltage measurements. It should be appreciated that themeter 100 may be arranged to determine power based on any otherconceptually similar pairs of voltages. For example, the meter 100 maybe arranged to determine power based on the determined voltages V_(AC),V_(BC) and V_(CN), where the phase conductor C is the common phaseconductor between the pairs of voltage measurements. Alternatively, themeter 100 may be arranged to determine power based on the voltagesV_(BA), V_(CA), and V_(AN), where the phase conductor A is the commonphase conductor between the pairs of voltage measurements. The skilledperson will appreciate that these alternative arrangements can beimplemented similarly to the arrangement described in the presentdisclosure, whilst having the same advantages.

In the present disclosure, it has been described how the FEC 200 doesnot comprise a current sensor between the neutral terminals 101N and102N. However, in some embodiments, the FEC may comprise a neutralcurrent sensor between the neutral terminals 101N and 102N. The neutralcurrent sensor may be similarly arranged to the current sensors betweenthe other terminals of the meter 100. The neutral current sensor mayoutput a voltage signal V_(IN)′ at its output nodes, where V_(IN)′ isindicative of the current I_(N) between the terminals 101N and 102N, andtherefore the current I_(N) on the conductor N when coupled to a neutralconductor. The output of the neutral current sensor may be coupled torespective differential inputs to the processing unit 300, so that theprocessing unit 300 may determine the neutral current IN similarly tohow it determines the other currents I_(A), I_(B), I_(C). Furthermore,in the embodiment of FIG. 5, the processing unit 300 may comprise anadditional ADC-IC for determining the neutral current I_(N). Thedetermined current I_(N) may be useful for detecting defects andtampering in relation to the power meter and/or the power line.

As described in the present disclosure, the voltage dividers or voltagetransformers provide signals at a measurable level that meets the safetyrequirements and maximum ratings of the components of the meter 100,such as the components of the processing unit 300. However, in somescenarios, the voltages on the conductors of the power line may alreadybe at a safe and measurable level. Therefore, in some embodiments, thevoltage dividers and voltage transformers may be omitted and theterminals of the meter 100 may be coupled directly to the respectivedifferential inputs of the processing unit 300 in order to measurevoltages V_(AB), V_(CB), and V_(BN).

In the present disclosure, the FEC 200/700 provides signals indicativeof currents and voltages on the power line in the form of voltagesignals V_(AB)′, V_(CB)′, V_(BN), V_(IA)′, V_(IB)′, or V_(IC)′. However,in some embodiments the FEC 200/700 may be arranged to provide one ormore of its output signals as current signals instead of voltagesignals, and the processing unit 300 may be configured to receivecurrent signals and perform power computations based on the receivedcurrent signals.

In the present disclosure, it has been described how the power meter 100is arranged to measure or determine instantaneous voltages and currentsof the power line that the power meter 100 is coupled to, and the powermeter 100 is configured to determine the power or various powerquantities on a power line based on the instantaneous voltages andcurrents. It should be appreciated that the power meter may beconfigured to determine any other suitable quantity or parameter inrelation to the power line. For example, the power meter 100 may beconfigured to determine one or more of the following quantities: energy(e.g. in Joules), kilo-watt hours (kWHrs), RMS currents/voltages, andpower factor. More generally, the meter 100 may be considered as anenergy meter configured to determine any of the above quantities. Theskilled person may apply any known or common techniques in order toconfigure the power meter 100 to determine the above quantities orparameters based on the measured instantaneous voltages and currents.

The present disclosure also provides a method comprising: coupling themeter 100 to conductors of a 3-wire or 4-wire three-phase power line;and setting the power meter 100 in the first mode in the event that themeter has been coupled to a 3-wire power line, or setting the powermeter 100 in the second mode in the event that the meter has beencoupled to a 4-wire power line. The method may further include, usingthe power meter, generating a plurality of signals indicative ofvoltages between at least two of the conductors, and determining thepower of the three-phase power line.

The appended claims are presented without using multiple dependencies,however, it should be understood that the various dependent claims (oraspects thereof) can be used in any permutation or combination withother claims, unless expressly indicated otherwise by the presentdetailed description in the specification.

The invention claimed is:
 1. A three-phase power meter, comprising: afront-end circuit (FEC) configured for coupling to a three wire or afour wire three-phase power line comprising a plurality of conductors,and to generate a plurality of signals indicative of voltages betweenrespective pairs of conductors; and a processing unit, coupled to theFEC, and configured to receive the plurality of signals, and todetermine the power of the three-phase power line; wherein the powermeter is configured to operate in a first mode, in order to determinethe power of a three wire three-phase power line, and in a second mode,in order to determine the power of a four wire three-phase power line;and wherein the FEC comprises a plurality of voltage generators, eachgenerator arranged to be coupled between a pair of conductors, and eachconfigured to generate at least one of the plurality of signalsindicative of voltages between respective pairs of conductors.
 2. Thethree-phase power meter of claim 1, wherein the plurality of voltagegenerators includes two voltage generators arranged to be coupledbetween respective pairs of phase conductors, and a voltage generatorarranged to be coupled between a phase conductor and a neutralconductor.
 3. The three-phase power meter of claim 1, wherein the FEC isconfigured to generate at least two signals indicative of voltagesbetween phase conductors of the three-phase power line, when the FEC iscoupled to either three or four wire power lines, and to generate atleast one signal indicative of a voltage between a phase conductor and aneutral conductor of the three-phase power line, when coupled to a fourwire power line.
 4. The three-phase power meter of claim 3, wherein: inthe first mode of operation, the processing unit is configured todetermine the power based on at least two of the signals indicative ofvoltages between phase conductors of the three-phase power line; and inthe second mode of operation, the processing unit is configured todetermine the power based on at least two of the signals indicative ofvoltages between phase conductors of the three-phase power line, and atleast one signal indicative of a voltage between a phase conductor and aneutral conductor of the three-phase power line.
 5. The three-phasepower meter of claim 3, wherein the FEC is configured to generate: afirst signal indicative of a voltage between a first phase conductor anda second phase conductor of a three-phase power line, when coupled to athree or four wire power line; a second signal indicative of a voltagebetween a third phase conductor and the second phase conductor of athree-phase power line, when coupled to a three or four wire power line;and a third signal indicative of a voltage between the second phaseconductor and a neutral conductor of the three-phase power line, whencoupled to a four wire power line.
 6. The three-phase power meter ofclaim 5, wherein: in the first mode of operation, the processing unit isconfigured to determine the power based on the first signal and thesecond signal; and in the second mode of operation, the processing unitis configured to determine the power based on the first, second andthird signals.
 7. The three-phase power meter of claim 6, wherein theFEC is further configured to generate a plurality of signals indicativeof currents on respective phase conductors of the three-phase powerline, and the processing unit is arranged to receive at least one of theplurality of signals indicative of currents and to determine power basedon receiving at least one of the signals indicative of the voltages andreceiving at least one of the plurality of signals indicative of thecurrents.
 8. The three-phase power meter of claim 1, wherein the FEC isfurther configured to generate a plurality of signals indicative ofcurrents on respective phase conductors of the three-phase power line,and the processing unit is arranged to receive the signals indicative ofcurrents and to determine power based on the received signals indicativeof the voltages and the received signals indicative of currents.
 9. Thethree-phase power meter of claim 8, wherein the FEC comprises: aplurality of current sensors for coupling to phase conductors of athree-phase power line, each current sensor configured to output asignal indicative of a current on the respective phase conductors. 10.The three-phase power meter of claim 1, wherein the FEC comprises: aplurality of terminals for coupling to respective conductors of athree-phase power line; wherein the plurality of voltage generatorsinclude a plurality of voltage dividers arranged between the terminals.11. The three-phase power meter of claim 10, wherein: the plurality ofterminals includes at least three phase-terminals for coupling torespective phase conductors of a three-phase power line, and at leastone neutral terminal for coupling to a neutral conductor of athree-phase power line; and the plurality of voltage dividers comprises:a first voltage divider arranged between a first phase terminal and asecond phase terminal; a second voltage divider arranged between a thirdphase terminal and the second phase terminal; and a third voltagedivider arranged between the second phase terminal and the at least oneneutral terminal.
 12. The three-phase power meter of claim 1, whereinthe FEC comprises: a plurality of terminals for coupling to respectiveconductors of a three-phase power line; wherein the plurality of voltagegenerators are a plurality of voltage transformers arranged between theterminals.
 13. The three-phase power meter of claim 1, wherein theprocessing unit is configured to receive user input to control anoperating mode of the three-phase power meter.
 14. The three-phase powermeter of claim 1, wherein the processing unit is configured toautomatically determine an operating mode of the three-phase power meterbased on at least one of the received plurality of signals.
 15. Afront-end circuit (FEC) for use in a three-phase power meter, the FECconfigured for coupling to a three wire or a four wire three-phase powerline comprising a plurality of conductors, and to generate a pluralityof signals indicative of voltages between respective pairs of conductorsof the three-phase power line, such that the three-phase power meterdetermines a power of the three-phase power line in a three wire firstmode, and determines a power of the three-phase power line in a fourwire second mode; and wherein the FEC further comprises a plurality ofvoltage generators, each generator arranged to be coupled between a pairof conductors, and each configured to generate at least one of theplurality of signals indicative of voltages between respective pairs ofconductors.
 16. The FEC of claim 15, wherein the plurality of voltagegenerators include two voltage generators arranged to be coupled betweenrespective pairs of phase conductors, and a voltage generator arrangedto be coupled between a phase conductor and a neutral conductor.
 17. TheFEC of claim 16, further comprising: a plurality of terminals includingat least three phase-terminals for coupling to respective phaseconductors of a three-phase power line, and at least one neutralterminal for coupling to a neutral conductor of a three-phase powerline; and the plurality of voltage generators comprise: a first voltagedivider arranged between a first phase terminal and a second phaseterminal; a second voltage divider arranged between a third phaseterminal and the second phase terminal; and a third voltage divider isarranged between the second phase terminal and the at least one neutralterminal.
 18. A method of determining a power measurement of a threewire or a four wire three-phase power line using a three-phase powermeter, the three-phase power line comprising a plurality of conductors,the method comprising: receiving, using a processing unit, a pluralityof signals, indicative of voltages between respective pairs ofconductors, received from a Front-End Circuit (FEC) comprising aplurality of voltage generators, each generator arranged to be coupledbetween a pair of conductors, and each configured to generate at leastone of the plurality of signals indicative of voltages betweenrespective pairs of conductors; determining whether the three-phasepower meter is coupled to a three wire power line or a four wire powerline; and processing the plurality of signals, using the processingunit, in order to determine the power measurement on the three-phasepower line, wherein the plurality of signals are processed dependentupon whether the three-phase power meter is coupled to a three wire orfour wire power line.
 19. A processing unit arranged to carry out themethod of claim 18.